The present invention relates to fuel compositions which yield reduced emissions and a method for reducing emissions in compression ignition engines burning said fuel compositions. According to the present invention it has been discovered that reduced particulate emissions, upon the burning of fuels, are obtained by the addition of low levels of a fuel additive, comprising mixtures of calcium salts with alkaline earth metal salts other than calcium salts and/or alkali metal salts, to the fuel.
Fuels used in compression ignition engines give off in the exhaust of the engine particulates which are harmful pollutants. These particulates include not only those that exist as visible smoke or soot when the engine is overloaded or when the engine is worn or dirty, but also those that are invisible and emerge from partly loaded clean engines. Particulates are solid materials expelled from the engine which typically have a size less than 100 microns, with the vast majority being 10 microns in size or less. Chemically, particulates will be composed of carbon, in the form of mixtures of partially oxidized carbon and hydrocarbon species; sulfur, mainly in the form of sulfates; and other non volatile components, such as metals from engine wear, lubricant oil, and parts of the additives themselves.
There have been many attempts at finding suitable smoke suppressants for use in middle distillate fuel compositions. See, for example, U.S. Pat. Nos. 3,410,670 and 3,413,102 and GB 888,325. Prior smoke suppressants include organic compounds of barium, particularly the barium carbonate overbased barium sulfonates, which are effective at substantially reducing the amount of smoke exhaust from an engine. However, there are serious questions concerning the use of barium compounds as smoke suppressants since barium compounds are known to be toxic upon ingestion by human beings at high dosages.
More recently, transition metal compounds, particularly manganese and iron, have been used for reducing smoke and other particulate emissions in the combustion of fuels. These transition metal compounds have been used alone or in combination with alkaline earth metals or alkali metals.
U.S. Pat. No. 4,207,078 discloses diesel fuel compositions containing manganese tricarbonyl compounds and oxygenated compounds. The reference does not teach the use of low levels of alkali metals and/or alkaline earth metals in reducing emissions.
European Patent No. 0 078 249 and GB 2 248 068 disclose additives with combustion-promoting and soot-inhibiting activity for combustion fuels. The additives are selected from transition metals, alkaline earth metals and mixtures thereof. The references requires the presence of a transition metal and thus do not teach the additive mixtures of the present invention.
U.S. Pat. Nos. 5,011,502 and 5,087,267 and European Patent Application No. 0394715 A1 disclose fuel additives derived from seawater. The additives contain mixtures of metal salts. However, these compositions contain elements, such as boron, silicon, iron, aluminum, chromium and titanium, which are not within the scope of the metals intended for use in the present invention.
WO 95/04119, WO 96/34074 and WO 96/34075 disclose fuel additives for reducing the emission of particulates comprising alkali, alkaline earth or rare earth complexes. The references fail to teach additives comprising the combinations of metals set forth in the present invention.
Currently, the United States Environmental Protection Agency (EPA) is proposing a de minimis provision for some atypical fuels and fuel additives (F/FAs), i.e., maximum concentrations or emission rates for atypical elements below which manufacturers of F/FAs containing such elements would be excused from some or all of the testing requirements for the product (Federal Register, Vol. 61, No. 134, Thursday, Jul. 11, 1996, pages 36535-36543). In the gasoline and diesel fuel families, an atypical F/FA is one which contains one or more elements other than carbon, hydrogen, oxygen, nitrogen and/or sulfur.
The EPA is proposing de minimis provisions applicable to the following nine elements: aluminum, boron, calcium, sodium, zinc, magnesium, phosphorus, potassium and iron. These nine elements were selected by evaluating a number of factors. First, any element known or believed to have significant inhalation-related health effects or to be a precursor to emission species of particular concern was eliminated as a candidate for the de minimis provision. For example, elements in the halogen family were eliminated because of their occurrence in toxic chemical species. Other examples include mercury, tin, and lead, which were eliminated from consideration because of their neurologic effects, and cobalt, platinum, silicon, and antimony, which were eliminated because of concerns about their potential respiratory effects in some chemical forms. Manganese was also eliminated because its health effects are still under study.
For the group containing the nine atypical elements it appears that limited exposures to ambient concentrations of at least 0.1 milligrams of the elements per cubic meter of air (mg/mm.sup.3) could occur without raising appreciable concerns. EPA estimates that a concentration of 25 parts per million (ppm) of atypical element(s) in a base fuel should generally yield a concentration in air of less than 0.1 mg/mm.sup.3. Thus, EPA is proposing a de minimis provision based on a qualifying level of 25 ppm in base fuel disregarding trace amounts of the elements which may exist in the unadditized fuel. Specifically, if an atypical additive contains no atypical elements other than the nine set forth above, and if the total of these elements added to the base fuel does not exceed 25 ppm by weight when the additive is mixed into the applicable base fuel at the highest treatment rate recommended by the additive manufacturer, then the additive (and F/FAs) mixture) would qualify for the de minimis provision.